Anaerobic waste water treatment provides a means for converting dissolved organic waste into methane and carbon dioxide. More particularly, anaerobic waste water treatment is often referred to as a pre-treatment process since the discharge from an anaerobic waste water treatment process often needs further treatment prior to discharge into the environment. Dissolved organic waste in a volume of waste water is often measured by “chemical oxygen demand” or “COD”. COD is usually given as a unit weight per unit volume or may be given as a unit weight in a given time period to rate the treatment capacity of a facility. COD reflects the amount of organic material by unit weight present in a unit volume of water.
An anaerobic waste water treatment process is particularly advantageous because only a small percentage of carbon and nitrogen in the organic waste is converted by the anaerobic microbial cultures into new cell mass. This results in far less waste material arising from the excess production of microbes. Moreover, the anaerobic digestion of waste can be conducted within a much smaller volume of space than with an aerobic process. Anaerobic waste water treatment is particularly adapted for treating the waste water produced by alcohol fermentation processes such as might be found in brewery or in a facility that produces fuel grade ethanol. Waste water produced by such facilities generally contains materials which can be most easily digested in an anaerobic process.
Typically, an anaerobic waste water treatment facility includes bioreactors, which are usually tanks having fluidized beds composed of many thousands of microbial granules containing colonies of microbes. These microbial granules are colonies consisting of various organisms. The microscopic organisms in these granules ingest organic waste and convert it primarily into methane and carbon dioxide. Other support equipment regulates the make up and the flow rate of the feed moving into and the products moving out of the bioreactors. Often, in anaerobic waste water treatment systems, some of the liquid product from the bioreactors is discharged from the system as treated water while most of the liquid product from the bioreactors is routed to a recycle tank. The recycle tank in such a system initially receives waste water for treatment and mixes it with recycled, treated water from the bioreactors. A recycle pump conveys the resulting mixture of waste water and recycled treated water to the bioreactors. The recycle tank can also be used as the place for conditioning the temperature, pH, and the nutrient content of the mixture entering the bioreactors in order to maintain the health of the above described microbial organisims. The bioreactors also produce carbon dioxide gas and methane gas. Methane gas does not dissolve in water and so it is collected at the top of the bioreactors. The methane gas can be routed to an outside process to help supply energy to that outside process or it can be flared off.
In the past, anaerobic waste water treatment systems have been constructed on site to meet the waste water treatment needs at that site. Typically, all of the components of the anaerobic waste water treatment system are sized, designed and constructed to meet the needs of the site. Since each component must be placed and installed on site, the cost of adding such a system capable of processing on the order of thousands of pounds of dissolved organic waste per day can be significant. Such a custom designed system would often require significant redesign in order to expand or enlarge a system to process larger amounts of waste. Accordingly, what is needed is a modular system that can be built off site, transported and then installed with a minimum of effort. A modular system is needed having standard support equipment capable of supporting the operation of between one and a significantly larger number of bioreactors so that bioreactors may be added at a later time with little additional cost.
Thus, there has long been a need in the industry, for a modular system for digesting organic waste that can be constructed and mostly assembled off site, transported and then installed at a desired location. There has also been a long felt need in the industry to have a modular system that is expandable to operate between one and a significantly larger number of bioreactors without having to change or modify other basic equipment in the modular system. Still further, there has been a long felt need in the industry to have a system that has its components placed within a small area so that an operator can access those components with an absolute minimum of time and effort.